(1) Field of the Invention
The present invention relates to a film jacket to be favorably used in receipt, arrangement and storage of a long strip film such as a microfilm, a negative film, a positive film, etc., and also suitably used for the projection of images of the film by a projector of, for instance, an overhead type while the film is being received therein.
(2) Description of the Prior Art
In general, the known film jackets for holding the long strip films are broadly classified into the following two types:
As shown in FIG. 10, one of the two types of the film jackets is a so-called loose type film jacket in which a surface sheet and a base sheet are welded together in the length direction of the long strip film A to be held therein and over a distance substantially corresponding to the entire length and the width W of the film pocket C formed between the adjacent joined portions B and B is designed considerably wider than the width w of the strip film A. The other is a so-called close type film jacket in which the width of the film pocket is designed slightly larger than that of the film.
Although the loose type film jacket has the advantage that the long strip film A can be easily inserted into the film pocket C because the width W of the film pocket C is considerably wider than the film width w, such a film jacket has the defects that the film in the film pocket C can not be accurately located, so that when the film images are projected while the film jacket holding, for instance, the positive films, is placed in the overhead type projector, it is practically impossible to always accurately locate the central portion of the positive film onto the optical axis of the projector and to completely eliminate the inclination of the image, and further that the strip film A is slipped away from the film pocket when the film jacket is carried. In addition, since the known jacket has a relative larger light permeation area of a zone consisting of the surface sheet 2 and the back sheet 4 and a zone consisting of sprocket holes positioned on both edges in the film width direction for winding up the film in the surrounding of the strip film held in the jacket, when the jacket is held up to the light source, a great amount of light beams leak from the light permeation area, so that the images become extremely difficult to see.
On the other hand, since the difference in the width between the film pocket and the film is slight in the case of the close type film jacket, there do not occur the problems mentioned in connection with the loose type film jacket after the long strip film is inserted into the film pocket. However, the close type film jacket has the drawbacks that it is not easy to insert the strip film into the film pocket, and even when the film-inserting direction is slightly different from the direction in which the film pocket is extended, the corner portion of the film is caught by the welded portion of the surface and back sheets, and consequently is bent thereby. Such problems are more serious in the case of the endscope film, the microfilm and the like in which the film width is far smaller as compared with the length of the film, and in the extreme case, a special assistant instrument is necessary to insert the films of these kinds into the film pockets. This makes the film-inserting operation more troublesome.